In conventional paint spray guns, a stream of paint under pressure is discharged from a relatively small orifice in a nozzle while air under pressure is discharged radially inwardly into the stream from an annular opening surrounding the nozzle closely adjacent the paint discharge orifice to atomize the stream of paint into a spray of fine particles. The spray thus produced moves away from the gun in an expanding conical pattern whose apex is at the nozzle.
It is frequently desired to modify the circular cross-section of the normal conical spray pattern by transforming this pattern into one of a narrowed and elongated generally elliptically shaped cross-section so that the spray pattern more closely resembles that of a flat sided fan.
In prior art spray guns, fanning of the spray pattern is typically accomplished by providing on the front of the air cap a pair of diametrically opposed ports spaced radially outwardly from opposite sides of the annular air discharge opening and oriented to direct air jets toward opposite sides of the spray pattern at a location spaced a short distance forwardly from the nozzle orifice. These jets have the effect of flattening the sides of the conical spray pattern against which they are directed. At any given distance from the nozzle, this action transforms the normally circular cross-section of the conical spray into a generally elliptically shaped cross-section whose major axis is somewhat greater than the original cone diameter and whose minor axis is somewhat less than the original cone diameter. The "flatness" of the elliptical cross-section will increase with an increase of the pressure at which air is expelled from the diametrically opposed fanning ports.
In prior art guns, adjustment of the fanning of the spray is typically made by rotatively adjusting the air cap. This adjustment exerts a valving action which establishes maximum air flow when the diametrically opposed valve ports lie in either a vertical plane containing the nozzle axis or a horizontal plane containing the nozzle axis. The flow from the fanning parts is reduced as the air cap is rotated to become zero when the fanning ports are midway between the horizontal and vertical positions referred to above. When the fanning ports are at this midway position, the spray assumes its original conical form.
While the foregoing arrangement provides for adjustment to the fanning of the spray, this adjustment is dependent upon the rotated position of the air cap about the nozzle axis. Adjustment of the fan width (minor axis of the elliptical fan cross-section) to a width between maximum or unmodified conical spray and minimum width requires the air cap to have its ports located in a general plane inclined from the vertical. This inclination of the fanning ports establishes the angle the major axis of the elliptical configuration will assume with respect to the vertical, a situation which is inconvenient to the operator who would prefer that this major axis be either vertical or horizontal for all degrees of fanning.
The present invention is directed to a spray gun in which fanning may be adjustably controlled completely independently of the rotative orientation of the air cap.